/*
 * Copyright (C) 2016-2018, Nils Moehrle
 * All rights reserved.
 *
 * This software may be modified and distributed under the terms
 * of the BSD 3-Clause license. See the LICENSE.txt file for details.
 */

/* Adapted for c from the example code provided in "Simplex noise demystified"
 * by Stefan Gustavson, Linköping University, Sweden (stegu@itn.liu.se).
 */

int grad3[][3] = {{1,1,0},{-1,1,0},{1,-1,0},{-1,-1,0},
    {1,0,1},{-1,0,1},{1,0,-1},{-1,0,-1},
    {0,1,1},{0,-1,1},{0,1,-1},{0,-1,-1}};

int p[] = {151,160,137,91,90,15,
    131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
    190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
    88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
    77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
    102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
    135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
    5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
    223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
    129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
    251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
    49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
    138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180};


int* perm = new int[512];

/* This method is a *lot* faster than using (int)Math.floor(x). */
int
fastfloor(double x) {
    return x > 0.0 ? static_cast<int>(x) : static_cast<int>(x) - 1;
}

double
dot(int g[], double x, double y, double z) {
  return g[0] * x + g[1] * y + g[2] * z; }

void
init (void)
{
    /* To remove the need for index wrapping, double the permutation table length. */
    for(int i = 0; i < 512; i++)
        perm[i] = p[i & 255];
}

/**
 * 3D simplex noise
 */
double
noise(double xin, double yin, double zin) {
    /* Noise contributions from the four corners. */
    double n0, n1, n2, n3;
    /* Skew the input space to determine which simplex cell we're in. */
    double F3 = 1.0 / 3.0;
    double s = (xin + yin + zin)*F3; // Very nice and simple skew factor for 3D
    int i = fastfloor(xin + s);
    int j = fastfloor(yin + s);
    int k = fastfloor(zin + s);
    double G3 = 1.0 / 6.0; // Very nice and simple unskew factor, too
    double t = (i + j + k) * G3;
    double X0 = i - t; // Unskew the cell origin back to (x,y,z) space
    double Y0 = j - t;
    double Z0 = k - t;
    double x0 = xin - X0; // The x,y,z distances from the cell origin
    double y0 = yin - Y0;
    double z0 = zin - Z0;
    /* For the 3D case, the simplex shape is a slightly irregular tetrahedron. */
    /* Determine which simplex we are in. */
    int i1, j1, k1; // Offsets for second corner of simplex in (i,j,k) coords
    int i2, j2, k2; // Offsets for third corner of simplex in (i,j,k) coords
    if(x0 >= y0) {
        if(y0 >= z0) { i1 = 1; j1 = 0; k1 = 0; i2 = 1; j2 = 1; k2 = 0; } // X Y Z order
            else if(x0 >= z0) { i1 = 1; j1 = 0; k1 = 0; i2 = 1; j2 = 0; k2 = 1; } // X Z Y order
            else { i1 = 0; j1 = 0; k1 = 1; i2 = 1; j2 = 0; k2 = 1; } // Z X Y order
        }
    else { // x0<y0
        if(y0 < z0) { i1 = 0; j1 = 0; k1 = 1; i2 = 0; j2 = 1; k2 = 1; } // Z Y X order
        else if(x0<z0) { i1 = 0; j1 = 1; k1 = 0; i2 = 0; j2 = 1; k2 = 1; } // Y Z X order
        else { i1 = 0; j1 = 1; k1 = 0; i2 = 1; j2 = 1; k2 = 0; } // Y X Z order
    }

    /*  A step of (1,0,0) in (i,j,k) means a step of (1-c,-c,-c) in (x,y,z),
        a step of (0,1,0) in (i,j,k) means a step of (-c,1-c,-c) in (x,y,z), and
        a step of (0,0,1) in (i,j,k) means a step of (-c,-c,1-c) in (x,y,z), where
        c = 1/6. */
    double   x1 = x0 - i1 + G3; // Offsets for second corner in (x,y,z) coords
    double   y1 = y0 - j1 + G3;
    double   z1 = z0 - k1 + G3;
    double   x2 = x0 - i2 + 2.0*G3; // Offsets for third corner in (x,y,z) coords
    double   y2 = y0 - j2 + 2.0*G3;
    double   z2 = z0 - k2 + 2.0*G3;
    double   x3 = x0 - 1.0 + 3.0*G3; // Offsets for last corner in (x,y,z) coords
    double   y3 = y0 - 1.0 + 3.0*G3;
    double   z3 = z0 - 1.0 + 3.0*G3;
    /* Work out the hashed gradient indices of the four simplex corners */
    int ii = i & 255;
    int jj = j & 255;
    int kk = k & 255;
    int gi0 = perm[ii + perm[jj + perm[kk]]] % 12;
    int gi1 = perm[ii + i1 + perm[jj + j1+perm[kk + k1]]] % 12;
    int gi2 = perm[ii + i2 + perm[jj + j2+perm[kk + k2]]] % 12;
    int gi3 = perm[ii + 1 + perm[jj + 1 + perm[kk + 1]]] % 12;
    /* Calculate the contribution from the four corners. */
    double t0 = 0.5 - x0 * x0 - y0 * y0 - z0 * z0;

    if (t0 < 0) n0 = 0.0;
    else {
      t0 *= t0;
      n0 = t0 * t0 * dot(grad3[gi0], x0, y0, z0);
    }
    double t1 = 0.5 - x1 * x1 - y1 * y1 - z1 * z1;
    if (t1 < 0) n1 = 0.0;
    else {
      t1 *= t1;
      n1 = t1 * t1 * dot(grad3[gi1], x1, y1, z1);
    }
    double t2 = 0.5 - x2 * x2 - y2 * y2 - z2 * z2;
    if (t2 < 0) n2 = 0.0;
    else {
      t2 *= t2;
      n2 = t2 * t2 * dot(grad3[gi2], x2, y2, z2);
    }
    double t3 = 0.5 - x3 * x3 - y3 * y3 - z3 * z3;
    if (t3<0) n3 = 0.0;
    else {
      t3 *= t3;
      n3 = t3 * t3 * dot(grad3[gi3], x3, y3, z3);
    }
    /* Add contributions from each corner to get the final noise value. */
    /* The result is scaled to stay just inside [-1,1] */
    return 32.0*(n0 + n1 + n2 + n3);
}

double
simplex_noise(double x, double y, double z, int octaves, double persistence) {
    double total = 0.0;
    double max = 0.0;
    double amplitude = 1.0f;
    double frequency = 0.03f;
    for (int i = 0; i < octaves; i++){
        frequency *= 2.0f;
        amplitude *= persistence;
        max += amplitude;
        total += noise(x * frequency, y * frequency, z * frequency) * amplitude;
    }
    return total / max;
}
